Using the web form

Click (Choose File) and select the Overview.src.html file on your local machine that you want to post-process (you should do this when you're ready to check it in).

Choose (*) Generated HTML - radio button

Click the (Submit) button

Save the page (e.g. in Firefox, choose the “Save Page as…” menu item from the “File” menu, be sure to choose “Web page, HTML only” from the “Save as” popup), name the file Overview.html (without the quotes), and save it right next your Overview.src.html - you'll likely be replacing an older version, that's ok, go ahead and confirm (command-R in the replace dialog).

Using a command-line script

If you're on a system with curl on it, just save the following line to a file somewhere in your executable path:

(Replace the USERNAME:PASSWORD with your W3C username and password, the same that you would enter when visiting the web form linked above.)

Mark the file as executable, then just run it from within the folder of the spec you're working on. It will automatically submit Overview.src.html to the post-processor and save the results to Overview.html.